Tag Archives: Active Directory

The title isn’t very descriptive. I recently came across a need to script adding users & groups to the “RequireMembershipOf” directive of PowerBroker Open. PowerBroker is a handy tool that really facilitates joining a Linux machine to a Windows domain. It has a lot of configurable options but the one I was interested in was RequireMembershipOf – which as you might expect requires that the person signing into the Linux machine be a member of that list.

The problem with RequireMembershipOf is, as far as I can tell, it has no append function. It has an add function which frustratingly erases everything that was there before and includes only what you added onto the list. I needed a way to append a member to the already existing RequireMembershipOf list. My solution involves the usage of bash, sed, and a lot of regex. It boils down to two lines of code:

Recently I came across a need to batch convert global security groups into universal security groups in my work’s Active Directory domain. The reason for this is so I could then turn them into Mail Enabled security groups, which would enable mail to be delivered to members of these groups. Unfortunately all security groups at this organization are Global in scope.

Seeing as this is a one domain organization there is no harm in changing the scope to Universal. Doing this via mouse is very tedious; fortunately we can use a few basic command line tools to automate the task. Thanks to Jeff Guillet for outlining how to do this.

The three magic commands are: dsquery, dsget, and dsmod.

First I wanted to test out a single security group to make sure everything would work. I couldn’t convert it because it was a member of several global security groups. This rabbit hole went several levels deep. Piping together dsquery, dsget, and dsmod all together solved this problem instantly:

The above command first gets the full name of the group specified by the -name command. The output is sent to the dsget command to query what groups that group is a member of. The output of that command is sent to the dsmod command, which does the work of actually changing each of those groups into a security group:

-c tells it to continue on error

-q tells it to not print successful changes.

-scope u instructs it to change the group’s scope to Universal.

Any errors will be printed to the console. Depending on how many levels of global groups there are you may have to run this command several times in order to convert the problematic groups to Universal scope.

Once that command finishes without error you can modify the group itself to be a universal group by simply omitting the middle dsget command:

After testing we are now ready to expand this to convert ALL Global security groups to be Universal in scope. If you would like a report of how many groups would be affected, run this command. It will output all groups from the query to the text file Groups.txt:

To modify every group simply omit the “-name” parameter from the group command used above with our test group. This will iterate through every group in the directory and pass it on to dsmod which will modify the scope to be universal:

dsquery group -limit 0 | dsmod group -c -q -scope u

Some built-in groups can’t be converted due to their nature, so you will have to work around those (Domain Users being one example.) You will probably need to run the command a few times until no errors appear.

I ran into enough snags when attempting to join an CentOS 6.6 machine to a Microsoft domain that I thought I would document them here. Hopefully it is of use to someone. The majority of the experience is thanks to this site.

Update 03/16/2015: I came across this site which makes things a little easier when it comes to initial configuration – messing with other config files is no longer necessary. The authconfig command to do this is below:

Replace DOMAIN with short domain name, FQDN with your fully qualified domain name, and Admin_account with an account with domain admin privileges, then skip to the Reboot section, as it covers everything before that.

After scratching my head for a while I came across this site, which explains that your krb5.conf is case sensitive – it must all be all upper case. Fixing my krb5.conf to be all caps for my domain resolved that issue.

Join the domain

net ads join domain.com.au -U someadadmin

When I tried to join the domain I received this lovely message:

Our netbios name can be at most 15 chars long, "EXAMPLEMACHINE01" is 16 chars long
Invalid configuration. Exiting....
Failed to join domain: The format of the specified computer name is invalid.

Thanks to Ubuntu forms I learned I needed to edit my samba configuration to assign an abbreviated NETBIOS name to my machine.

vi /etc/samba/smb.conf

Uncomment the “netbios name =” line and fill it in with a shorter (max 15 characters) NETBIOS name.

netbios name = EXAMPLE01

You can test to ensure the join was successful with this command

net ads testjoin

Configure home directories

The authconfig command above included a switch for home directories. Make sure you create a matching directory and set appropriate permissions for it.

mkdir /home/DOMAIN
setfacl -m group:"Domain Users":rwx /home/DOMAIN #the article calls to do this, this command doesn't work for me but home directories still appear to be created properly

Reboot

To really test everything the best way is to reboot the machine. When it comes back up, log in with Active Directory credentials. It should work!

Account lockout issues

I ran into a very frustrating problem where everything works dandy if you get the password correct on the first try, but if you mess up even once it results in your Active Directory account being locked. You were locked out after the first try. Each login, even when successful, had this in the logs:

winbind pam_unix(sshd:auth): authentication failure

This problem took a few days to solve. Ultimately it involved modifying two files:

vi /etc/pam.d/system-auth
vi /etc/pam.d/password-auth

As far as I can tell, the problem was a combination of pam_unix being first (which always failed when using AD login), as well as having both winbind and kerberos enabled. The fix was to change the order of each mention of pam_unix to be below any mention of pam_winbind. The other fix I had to do was to comment out mentions of pam_krb5 completely.

#auth sufficient pam_krb5.so use_first_pass

Restrict logins

The current configuration allows any domain account to log into the machine. You will probably want to restrict who can log in to the machine to certain security groups. The problem: many Active Directory security groups contain spaces in their name, which Linux doesn’t like.

How do you add a security group that contains a space? Escape characters don’t seem to work in the pam config files. I found out thanks to this site that it is easier to just not use spaces at all. Get the SID of the group instead.

Use wbcinfo -n to query the group in question, using the backslash to escape the space. It will return the SID we desire.

Configure sudo access

Sudo uses a different list for authorization, which amusingly, handles escaped spaces just fine. Simply add the active directory group in sudo as you a local one, eg using a % and then group name, escaping spaces with a backslash:

%Domain\ Users ALL=(ALL) ALL

Rejoice

You’ve just gone through a long and painful battle. Hopefully this article helped you to achieve victory.

I had posted here about how to extract account names with a specific modifier (exclude account names ending in a dollar sign.) That worked for one specific instance, but I found I needed something better. Active Directory logs have multiples of the same value (Account_Name, Group_Name, etc.) that all depend on context, namely the value of the line two lines above it.

You can see that there are three different Security ID fields, three different Account Name fields, and two different Account Domain fields. The key is the context: Subject account name, member account name, or group account name.

I wrestled for some time to find a regex expression for Splunk that would continue matching things after a line has ended. After much searching I came across this post which explained the need for a regex modifier to do what I wanted.

In my case I needed to use the (?s) modifier to include newline characters in my extraction. My new and improved AD regex extraction is as follows:

(?s)(Group:.+Account Name:\s+)(?P<real_group_name>[^\n]+)

(?s) Regex modifier indicating to include new lines

Group: Section I am interested in. You can replace this with Member: if you’re interested in member account names instead

.+ match one or more of any character (including new line as indicated by modifier above)

Account Name:\s+ This is in conjuction with the previous two items to create a match that includes the section name and anything after that until the spaces after Account Name

[^\n]+ Match one or more characters that is not a new line (since you might have an account name with spaces.)

I don’t really understand Microsoft’s rationale when it comes to log verbosity. I suppose too much information is better than not enough information, but that comes at the cost of making it difficult if you have to try and actually read the information.

I’ve been trying to extract usernames from Active Directory controller logs and it turned out to be quite a pain. Why do the logs have more than one field with the same name? It confuses Splunk and seems to fly in the face of common sense and decency.. I will stop ranting now.

In my specific case, AD lockout logs have two Account Name fields, one for the controller and one for the user being locked out. I am interested only in the username and not the AD controller account name. How do you tell Splunk to only include the second instance of Account Name?

The answer is to create a field extraction using negative lookahead (Thanks to this article which gave me the guidance I needed.) I had to tweak the regex to look for and exclude any matches ending in a dollar sign, as opposed to excluding dashes in the article’s example. My fine tuned regex statement is below:

Account Name:\s+(?!.+\$)(?P<FIELDNAME>\S+)

It looks for Account Name: followed by one or more spaces (there is excess spacing in the logs for some reason.) The real magic happens in the next bit – (?!.+\$)

Parenthesis group the expression together

?! means negative lookahead – don’t include anything you find that matches the following regex

.+ – one or more characters

\$ – stop matching when you encounter a dollar sign

The second regex string is simply \S+ (one or more non-whitespace characters.)

Note this doesn’t satisfy all AD logs, just the ones I’m interested in (account lockouts – they all have a first Account Name ending in a dollar sign.)

The result of all this jargon and gnashing of teeth: clean Splunk logs revealing only what I want without excess information. Neat.

Update: I found an even better way to do this. The key is to use the regex modifier (?s) to include new lines. The better query is now this:

(?s)(<section name of the field you're interested in>:.+Account Name:\s+)(?P<real_group_name>[^\n]+)